How to integrate Auth0 login on Desktop Office apps (in an Addin)

Hello,

I am currently developing an Addin for Word and it is difficult to finish it because the SSO (Auth0) is working well on the web version and my plugin works wonders however I cannot login on the Windows or Mac version of Word because of the url mismatch as I do not own the Auth0 domain.

I quote: "Your add-in can use a middleman service such as OAuth.io or Auth0 to perform authorization. A middleman service may either provide access tokens for popular online services or simplify the process of enabling social login for your add-in, or both. With very little code, your add-in can use either client-side script or server-side code to connect to the middleman service and it will send your add-in any required tokens for the online service. All of the authorization implementation code is in the middleman service.

We recommend that the UI for authentication/authorization in your add-in use our Dialog APIs to open a login page." and when I click on the link here: https://video2.skills-academy.com/en-us/office/dev/add-ins/develop/auth-with-office-dialog-api it tells me to use the Office dialog api. On that page I read: "The host page and the resource that opens in the dialog box must have the same full domain. If you attempt to pass displayDialogAsync a subdomain of the add-in's domain, it will not work. The full domain, including any subdomain, must match. "
My current problem is that it works well on the Web version but the popup does not open on Mac at all because auth0 does not allow custom domain -> https://community.auth0.com/t/customize-login-page-when-using-authentication-api-with-pkce/88171/3

How should I allow my users to login through the desktop app (on Auth0) in my Addin? What other solution is there as my backend runs with Auth0 for everything.

Thanks for your help